An intriguing new theory suggests that seagrass growing in the immediate vicinity of a coral reef may be able to mitigate ocean acidification.
Research due to be published as a paper in the Open Access Environmental Research Letters journal, found that the high photosynthetic rates of seagrass meadows can make seawater less acidic and potentially enhance the growth of nearby corals, helping to preserve the world’s most beautiful and fragile coral reefs from extinction due to ocean acidification.
The research was conducted by Dr Richard Unsworth, Research Officer at the Centre for Sustainable Aquatic Research, College of Science, Swansea University in collaboration with scientists at the University of Oxford, the Northern Fisheries Centre, Australia, and James Cook University in Australia.
Explaining the background to the study Dr Unsworth said: “Highly productive tropical seagrasses often live adjacent to or among coral reefs and photosynthesise at such rates you can see the oxygen they produce practically bubbling away. We wanted to understand whether this could be a major local influence on seawater and the problems of ocean acidification.”
Rising atmospheric carbon dioxide (CO2) in the air, primarily from human fossil fuel combustion, reduces ocean pH and causes wholesale shifts in seawater carbonate chemistry. Over long-term timescales, this change in seawater carbonate chemistry is likely to cause coral reefs to start to disappear as the rate of erosion starts to exceed growth rates. Coral reefs house thousands of unique species that are found nowhere else on the planet. They provide physical protection for small island communities, and provide food for millions of people globally. Losing these reefs would have serious negative economic and food security consequences.
Dr Unsworth explained that their research models have shown remarkable results. He said: “Our analyses show that in shallow water reef environments coral calcification downstream of seagrass has the potential to be 18% greater than in an environment without seagrass. It illustrates the importance of keeping seagrass meadows healthy and offers a potential tool in marine park management to offset the impacts of ocean acidification (depending on local conditions and habitats)”. He added “Not only are seagrass meadows important to hundreds of millions of people worldwide who are dependent upon the food resources that they supply, our novel study suggests that they could potentially, in the long-term, have the added benefit of enhancing the growth of coral reefs under threat of extinction”.
Adapted from material on the Swansea University website.
A Poor Show from the BBC
The BBC is normally excellent when reporting science stories, but when covering this story managed to miss-describe corals as being, “… worm-like creatures of around a centimetre length which live in colonies numbering millions…”
In the Reef Aquarium
The rise in pH described by the researchers can also occur under aquarium conditions. If macro algae start to proliferate to the extent that it grows out of control it can result in pH increasing values of 9 and higher. Remember that the pH scale is logarithmic so a reading of say 9.2 is ten times more alkaline than the more usual reef aquarium value of 8.2. The higher the pH value, the greater the toxicity of any free ammonia that’s present. To correct this problem add CO2 to the system until the pH drops to the correct value. The various CO2 reactors designed for CO2 fertilization in the freshwater-planted aquarium are ideal for this purpose. Follow this up by harvesting excess macro algae until balance is restored and CO2 is no longer needed.